Two goals in less than two minutes at the end of the first half put Manchester United on their way to an easy victory at Leicester City as the Premier League champions' relegation worries deepened.

A largely drab first period -- in which the visitors' Marcus Rashford saw a low effort superbly tipped away by goalkeeper Kasper Schmeichel and home skipper Wes Morgan had a dangerous header blocked -- had seemed set to fizzle out into a goalless half-time scoreline.

But a moment of quality from Henrikh Mkhitaryan changed all that after 41 minutes when he controlled a Chris Smalling header and got away from Robert Huth, racing into the penalty area before firing a powerful finish into the top corner off Schmeichel.

Seconds later it was 2-0 as Zlatan Ibrahimovic -- central to many of United's best moments -- took advantage of more hesitation in the home defence to sweep home a finish after Antonio Valencia's skimming low cross had found him unmarked.

By that stage United were arguably fortunate to still have 10 men on the pitch after Juan Mata was booked for a clattering challenge on Jamie Vardy for which he could well have seen red -- and the midfielder was on hand to wrap up the match just three minutes into the second period.

Home manager Claudio Ranieri made two changes at the break, taking off Ahmed Musa and Shinji Okazaki for Demarai Gray and Andy King, with Manchester United bringing off Marcos Rojo and replacing him with Daley Blind.

But Ranieri and Leicester saw their hopes of salvaging anything from another worrying afternoon disappear when Mata played a one-two with Mkhitaryan and finished coolly beyond the exposed Schmeichel, with the stranded Morgan playing him well onside.

The home goalkeeper prevented United from making it four soon afterwards with a smart save from Rashford as Leicester continued to offer virtually nothing at the other end, although Riyad Mahrez did brush the side netting with one curling free kick.

Mata could have doubled his tally when a ball over the top found him in acres of space with the home defence nowhere, but he was unable to lift his attempted finish over Schmeichel.

Vardy flicked a header well over the top as Leicester continued to fail to ask any really threatening questions, and Jose Mourinho substituted Mata and replaced him with Marouane Fellaini with 15 minutes remaining.

A late Gray effort deflected wide for a thoroughly demoralised home team before a long-range Paul Pogba effort was clutched by Leicester and the game ended to a chorus of boos from the home crowd.